This invention relates to a novel zoom lens and image pickup apparatus, and more particularly to a zoom lens and an image pickup apparatus suitable for use with a camera such as a video camera or a digital still camera wherein an image pickup device is used to receive light to pick up an image.
Zoom lenses of various zoom types have been, in the past, used for video cameras.
One of such zoom lenses as mentioned above is disclosed, for example, in Japanese Patent Laid-open No. 2000-121938 (hereinafter referred to as Patent Document 1). The zoom lens disclosed in Patent document 1 adopts a five-group configuration having positive, negative, positive, positive and negative lens groups. In particular, the zoom lens includes a first lens group having a positive refracting power, a second lens set having a negative refracting power, a third lens group having a positive refracting power, a fourth lens group having a positive refracting power, and a fifth lens group having a negative refracting power, disposed in order from the object side.
In an optical system having a high zoom ratio, the angle of view in a telephoto end state is narrow, and therefore, a large blur occurs with an image even by a small hand shake. Therefore, a video camera particularly having a high zoom ratio incorporates an electronic hand shake correction system wherein an image fetching range of a light receiving device is shifted so as to correct a hand shake.
Further, a hand shake correction optical system has been, in the past, known wherein some lens group which is a component of a lens system is shifted in a direction substantially perpendicular to the optical axis of the lens system to compensate for deterioration of the optical performance which occurs when an image position is shifted.
The hand shake correction optical system can function as an optical hand shake correction system which includes a combination of a detection system for detecting a shake of a camera caused by such a hand shake as may arise, for example, from a shutter release, a control system for providing a correction amount to the lens position based on a signal outputted from the detection system and a driving system for shifting a predetermined lens based on an output of the control system.
With the optical hand shake correction system described above, it is possible to shift an image by shifting of the predetermined lens by means of the driving system, and blur of an image caused by a shake of the camera can be corrected by shifting of the predetermined lens by the driving system.
Such a hand shake correction optical system as just described is disclosed, for example, in Japanese Patent Laid-open No. 2002-244037 (hereinafter referred to as Patent Document 2), Japanese Patent Laid-open No. 2003-228001 (hereinafter referred to as Patent Document 3) or Japanese Patent Laid-open No. 2003-295057 (hereinafter referred to as Patent Document 4).
In the zoom lens disclosed in Patent Document 2, a third lens group disposed on the image side of an aperture stop includes a negative sub group and a positive sub group, and the positive sub group is shifted to shift an image.
In the zoom lens disclosed in Patent Document 3, a third lens group disposed on the image side of an aperture stop includes a positive sub group and a negative sub group, and the positive sub group is shifted to shift an image.
In the zoom lens disclosed in Patent document 4, an entire third lens group is shifted to shift an image.
In the hand shake correction optical systems described, a shift of an image caused by a hand shake or the like is corrected based on a blur correction coefficient.
Where the focal distance of the entire lens system is represented by f and the hand shake angle is represented by θ, the image shift amount yb by a hand shake is calculated in accordance withyb=f·tan θThe lens shift amount SL necessary to correct the image shift amount yb is given bySL=−f·tan θ/βswhere βs is the blur correction coefficient. Therefore, as the blur correction coefficient βs increases, a hand shake can be corrected with a smaller lens shift amount SL.